Method of preparing antifoaming agent

ABSTRACT

The activity of hydrophobic silica antifoamers in an oil dispersion is greatly enhanced by the presence of a polyfluorosilicate.

O Unlted States Patent 1151 3,639,260 Michalski 1 Feb. 1, 1972 [54] METHOD OF PREPARING [56] References Cited ANTIFOAMING AGENT UNITED STATES PATENTS [72] Invent Raymnd 2,802,850 8/1957 Wetzel .252/313 x [73] Assignee: Nalco Chemical Company, Chicago, Ill. 2,891,875 6/1959 Phreaner. ...252/313 X 3,076,768 2/1963 Boylan ..252/358 1221 Flled= APP-16,1969 3,267.042 8/l966 Domba ..252/358 x 211 App]. No.: 816,796 3,359,294 [2/1967 Domba .252/321 x Primary Examiner-Richard D. Lovering Attorney-Kinzer, Dom & Zickert, John G. Premo. Charles 52] us. 01. ..252/358, l06/308 Q, 1 17/100 s, and

117/123 c, 252/309, 252/321 57 ABSTRACT 511 1m. (:1. ..B0ld 19/04, BOlj 13/00 I l [58] Field of Search .252/321, 358, 309, 313 s; The acfivily of hydrophobic silica antifoamers in an Oil p sion is greatly enhanced by the presence of a polyfluorosilicate.

2 Claims, No Drawings METHOD OF PREPARING ANTIFOAMING AGENT This invention relates to an antifoaming agent in the form of hydrophobic silica to which a polyfiuorosilicate is attached or combined therewith to enhance antifoam action.

Foaming of a liquid stock is often responsible for certain inefficiencies notably in the paper pulp industry, in the manua.

facture of latex paints, and in the recovery of unused monomers during production of synthetic rubber. It is known to reduce foaming in various liquid systems by treatment with in U.S. Pat. No. 3,408,306; another mode of attaining hydrophobocity is disclosed herein in terms of an emulsion technique, constituting the subject matter of the copending application of Roger W. Youngs, Ser. No. 8 5,646, filed Apr. I6, 1969.

In accordance with the present invention, and as theprimary object thereof, the ability of hydrophobic silicas to reduce foaming is greatly enhanced by combining it with a polytetrafluorosilicate and more specifically that which is the reaction product of polyethyl silicate and polytetrafiuoroethylene. The silica may beof'the ordinary precipitated form, rendered hydrophobic by a suitableagent, or it may be prepared in accordance with the Youngs disclo sure.

The preferred method of producing the product of the present invention is to start with silica in an aqueous medium emulsified in a suitable oil as disclosed in the copendingapplication of Roger W. Youngs. The source of silica may bea hydrosol, or sodium silicate dissolved in water, each of which v is characteristic of a hydrophilic silica. The hydrophilicsilica. is rendered hydrophobic by attaching a hydrophobic surfactant to the silica-OH groups, and water is strippedfrom the system in accordance with the Youngs disclosure. The resultant product, hydrophobic silica of extremely small particle size dispersed in an oil, itself displays remarkable an tifoaming propensity, and in accordance with the present in vention this propensity may be increased by addition of a polytetrafiuorosilicate. Example 1 to follow presents the preferred method of obtaining the present product,

The fluoro-silicate polymer is preferably that of U.S. Pat. No. 3,359,294, being the reaction product of polytetrafiuoroethylene and polyethyl silicate.

l. The reactor, topped by a condenser, is charged with paraffin oil (the dispersing medium), silicone oil, glyceride and stearic acid, with agitation. The free-board area within the reactor is then subjected to a vacuum of 100-150 mm. Hg.', whereupon the reactor is charged with the silica sol while continuing to agitate the mixture. ll. While maintaining the vacuum, and keeping the temperature within a 60-65 C. range, water is slowly distilled from the emulsion, continuing agitation. The temperature will begin to rise when the water has been removed. Vacuum is maintained until a temperature of I60 C. is reached,whereupon the vacuum is broken by admission of nitrogentothe freeboard area-The temperature of the mixture is raised to 250 C., held for 4 hours to cause the silicone oil to attach to the silica particles, and then cooled to room temperature. The product thus obtained is useful as an antifoaming agent, but the activity thereof is greatly increased by stage III.

Ill. The productfrom stage ll is cooled to about 40 C., whereafter the fiuorosilicate polymer is added, resulting in an end product of enhanced antifoaming activity as hereinafter shown, but one which is preferably subjected to homogenization treatment. The yield is 965 to 980 pounds, depending upon the reactor efficiency.

While the silicone oil is preferably the one specified, any othersilicone oil presenting alkyl or .phenyl groups may be used.

Preferably, the hydrosol is of .small particle size, five millimicrons or less particle (average) diameter, and hence a sodium silicate. solution may also be used, provided it is acidified to a pH of about 3-l0 in situ during emulsification. The concentrationv of silica in the aqueous medium, in any event, is one of choice, and one need only use enough oil (paraffin oil or mineral seal oil or both) and emulsifier to obtain micelle formation. Superior emulsification is obtained whenusing both the glyceride and stearic acid, but other emulsifying agents may be used, as disclosed in the Youngs application, incorporated herein by reference.

When water is strippedfrom the emulsion system, the silicone oil renders the silica completely hydrophobic, the silicone attaching-itself to the colloidal silica particles as the mixture is heated. .Homogenization is simply to assure that a highly dispersed state is indeedattained.

In any event, the end product at stage ll may be classified as an emulsion-prepared.hydrophobic silica-silicone oil complex (product ll hereinafter) and the product of stage III may be classifiedas a hydrophobic silicasilicone oil-polyfluorosilicate complex (product lll hereinafter) in which the antifoaming activity is enhanced by the fiuorosilicate polymer as will be shown. Anitfoaming superiority of product ll is shown in the Youngs application. Under the present invention, antifoaming capability of a hydrophobic silica is enlarged as will be now discussed in terms of a very severe foaming circumstance in the paper pulp industry.

Conditionsfor pulp manufacture not only vary from the standpoint of stages within the mill itself, but also any set of given processing conditions for paper manufacture can vary throughout a wide geographical area. The efficiency of an antifoaming agent of this invention was tested at a pulp processing mill in tenns of its ability to render the pulp system more susceptible to effective washing treatment. Thus, as an economic measure, pulps are subjected to a washing action at an appropriate stage of processing in order to recover certain chemicals used for pulp treatment; However, foaming, characterizing the entrainment of air in the pulp slurry, decreases washing efficiency, and .the prevalence of entrained air can be diminished by addition of an antifoaming agent.

It is customary to test washing efficiency by withdrawing a sample of the pulp and squeezing water therefrom. The amount of dissolved solids is measured by electrical conductivity. The less the amount of dissolved solids in the water squeezed from the pulp, the greater the washing efficiency. There are thus two factors susceptible of determination, the degree of foaming in-the first instance and, separately, the measureof dissolved solids in the water squeezed from the pulp as ameasure .ofantifoam activity.

Under thisteshboth product ll and product lll produced in accordancewith example] were used as antifoaming agents, along withothers, table l and while product ll failed in spite of its exceptional performance independently in other foam environment, it must be understood that (the foam circumstances of the test here reported in table I were severe:

3 TABLE 1 Antifoam Agent Dissolved Solids, p.p.m.

Agents lD-7-8 and D-24 in table 1 represent commercially available grades of hydrophobic silicas, themselves dispersed in an oil as a carrier; lD-7-8A and D-24A are the same silicas to which was added 2 percent by weight of the above identified tetrafluorosilicate polymer, the synergistic effect of which was confirmed by independent testing producing the results in table 2:

TABLE 2 Amount to control fnam Agent (milliliters) A 135 A+2%' 90 B 126 B+l%' 75 D I05 Dl-l'lo' 70 is I: by weight ofthe copolymer of polyethyl silicate and pclytetrafluoroethylene The agents A, B and D were samples of commercially available hydrophobic silica, dispersed in a paraffin oil. The amount to control the foam was that required to hold the foam to a standard volume, such that a decreasing amount signifies increasing activity of the foam control agent. In each instance the presence of the tetrafluorosilicate polymer was responsible for a marked increase in efficiency.

It will be seen from the foregoing that under the present invention the antifoam activity of hydrophobic silicas is increased remarkably by addition of a small amount of the copolymer of polytetrafluoroethylene and polyethyl silicate which need be no more than about 2 percent by weight of the silica. Preferably, the silica is an emulsion prepared silica, giving the highest activity under some circumstances, but the invention may also be applied to precipitated silicas.

What is claimed is:

l, A method of preparing an antifoaming agent in the form of 'a hydrophobic silica sol comprising, emulsifying in an oildispersing medium an aqueous system of hydrophilic silica in the presence of a surfactant capable of bonding to the OH groups of the hydrophilic silica to render the latter hydrophobic, stripping water from the emulsified system resulting in an oil dispersion of the hydrophobic silica, and adding an effective amount of tetrafluorosilicate polymer sufficient to increase the antifoaming property of the resultant product, said polymer being the reaction product of a polytetrafluorethylene telomer having an average molecular weight of at least approximately 500 and a polyethyl silicate, reacted at a temperature of from l00-300 C. for a period of from about 2 to 20 hours.

2. A method according to claim 1 in which the hydrophilic silica is a silica hydrosol of no greater than about 5 millimicrons particle size, in which the dispersing medium is selected from the group consisting of paraffin oil and mineral seal oil, and in which the surfactant is a silicone oil.

CERTIFICATE OF CORRECTION Patent No. 3,639,260 Dated February 1, 1972 Raymond J. Michalski It is certified that errors appear in the above identified patent and that said Letters Patent are hereby corrected as shown below:

In the Specification:

Column 1, line 59, in Example 1, under "Percent by Weight" column should be O.95 and under "Charge (lbs.) column should be Signed and sealed this 25th day of July 1972.

(SEAL) Attest:

ROBERT GOTTSCHALK Commissioner of Patents EDWARD lmFLEwcrm-R ,JR Attesting Officer MW 4. iw

CERTIFICATE OF CORRECTION Patent No. 3, 639, 260 Dated February 1, 1972 Raymond J. Michalski It is certified that errors appear in the above identified patent and that said Letters Patent are hereby corrected as shown below: I

In the Specification:

Column 1, line 59, in Example 1, under "Percent by Weight" column should be O.95- and under "Charge (lbs.) column should be Signed and sealed this 25th day of July 1972.

(SEAL) At'test:

ROBERT GOTTSCHALK Commissioner of Patents EDWARD ZILFLETCHER JR Attesting Officer 

2. A method according to claim 1 in which the hyDrophilic silica is a silica hydrosol of no greater than about 5 millimicrons particle size, in which the dispersing medium is selected from the group consisting of paraffin oil and mineral seal oil, and in which the surfactant is a silicone oil. 